Post Paid Company

So my phone shows UNKNOWN when anyone phones me. I phone 082111 just for them to tell me that i need to phone my contract supplier 'Post paid company' .... I have NEVER even heard of this company and i havent had any contracts in over 13 years ..... so now its up to me to sort out this issue .... i bought a PREPAID sim over a year ago, now i must phone al over the country to solve this issue. and its not even my issue WHAT THE HELL!!!